Problem 32: Pandigital products

We shall say that an n-digit number is pandigital if it makes use of all the digits 1 to n exactly once;
for example, the 5-digit number, 15234, is 1 through 5 pandigital.

The product 7254 is unusual, as the identity, 39 * 186 = 7254, containing multiplicand, multiplier, and product is 1 through 9 pandigital.

Find the sum of all products whose multiplicand/multiplier/product identity can be written as a 1 through 9 pandigital.HINT: Some products can be obtained in more than one way so be sure to only include it once in your sum.

My Algorithm

We have to solve an equation a * b = c.
There are 9!=362880 permutations of { 1,2,3,4,5,6,7,8,9 } and for each of those permutation I try all possible combinations of a, b and c.

All digits (0..9) are stored in a plain std::vector and the STL's function std::next_permutation generates all permutations.
Then two nested loops split the sequence into three parts (a has length lenA, b has length lenB and c has length lenC).
If a * b = c then my program stores the product c in std::set named valid. Duplicates are automatically avoided by the std::set.

Changelog

Hackerrank

Difficulty

5%
Project Euler ranks this problem at 5% (out of 100%).

Hackerrank describes this problem as easy.

Note:Hackerrank has strict execution time limits (typically 2 seconds for C++ code) and often a much wider input range than the original problem.In my opinion, Hackerrank's modified problems are usually a lot harder to solve. As a rule thumb: brute-force is rarely an option.

Those links are just an unordered selection of source code I found with a semi-automatic search script on Google/Bing/GitHub/whatever.
You will probably stumble upon better solutions when searching on your own.
Maybe not all linked resources produce the correct result and/or exceed time/memory limits.

Heatmap

Please click on a problem's number to open my solution to that problem:

green

solutions solve the original Project Euler problem and have a perfect score of 100% at Hackerrank, too

yellow

solutions score less than 100% at Hackerrank (but still solve the original problem easily)

gray

problems are already solved but I haven't published my solution yet

blue

solutions are relevant for Project Euler only: there wasn't a Hackerrank version of it (at the time I solved it) or it differed too much

orange

problems are solved but exceed the time limit of one minute or the memory limit of 256 MByte

red

problems are not solved yet but I wrote a simulation to approximate the result or verified at least the given example - usually I sketched a few ideas, too

black

problems are solved but access to the solution is blocked for a few days until the next problem is published

[new]

the flashing problem is the one I solved most recently

I stopped working on Project Euler problems around the time they released 617.

The 310 solved problems (that's level 12) had an average difficulty of 32.6&percnt; at Project Euler and
I scored 13526 points (out of 15700 possible points, top rank was 17 out of &approx;60000 in August 2017)
at Hackerrank's Project Euler+.

My username at Project Euler is stephanbrumme while it's stbrumme at Hackerrank.

Copyright

I hope you enjoy my code and learn something - or give me feedback how I can improve my solutions.All of my solutions can be used for any purpose and I am in no way liable for any damages caused.You can even remove my name and claim it's yours. But then you shall burn in hell.

The problems and most of the problems' images were created by Project Euler.Thanks for all their endless effort !!!

more about me can be found on my homepage,
especially in my coding blog.
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